1. Field of the Invention
The present invention relates to a composite reverse osmosis membrane and also to a process for producing the same. More particularly, the present invention relates to a reverse osmosis membrane which is composed of a microporous support and a thin layer of crosslinked polyamide formed thereon and permits a high flux as well as a high salt rejection, and also to a process for producing the same.
2. Description of the Prior Art
There are several kinds of reverse osmosis membranes, for example asymmetric reverse osmosis membranes, and composite reverse osmosis membranes. The latter is composed of a microporous support layer and an active thin layer formed thereon which is capable of selective separation. It is usually produced by forming on a support layer a thin layer of polyamide which is obtained by interfacial polymerization of a polyfunctional aromatic amine and a polyfunctional aromatic acid halide. (See Japanese Laid-open Patent Application Nos. 147106/1980, 121603/1987, 218208/1988, and 187135/1990). The polyamide thin layer may also be obtained by interfacial polymerization of a polyfunctional aromatic amine and a polyfunctional alicyclic acid halide. (See Japanese Laid-open Patent Application Nos. 258705/1987 and 218208/1988).
What is most important technically and economically in desalination of brine and seawater by reverse osmosis is the salt rejection and the flux. The former denotes the ability of the reverse osmosis membrane to reduce the salt concentration in the solution emerging from the membrane. The latter denotes the flow rate of the water which passes through the membrane. For practical desalination by reverse osmosis, the flux should be higher than about 0.4 m.sup.3 /m.sup.2 -day at 55 atm in the case of seawater and about 0.6 m.sup.3 /m.sup.2 -day at 15 atm in the case of brine.